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Latest Treatments for Retinitis Pigmentosa

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Argus II vs OUReP

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Retinitis pigmentosa is inherited degeneration of the retina and retinal pigment epithelium.  Symptoms of this disease include night blindness, loss of peripheral vision, and decrease of visual acuity.

 

The retina includes two types of photoreceptor cells that are cone cells and rod cells.  Cone cells are concentrated in the macula at the center of the retina and are responsible for visual acuity and color vision.  Since cone cells are less sensitive to light, they do not function at a dark place.  In contrast, rod cells are concentrated at the outer edges of the retina and are responsible for peripheral vision.  Since rod cells are more sensible to light, they function at a dark place.

 

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Argus II.  Image Source:  Second Sight

 

In the early stage of retinitis pigmentosa, retinal rods are affected, causing defective night vision.  In the middle stage, night vision may eventually be lost.  In the advanced stage, a peripheral ring scotoma widens gradually and central vision may also be affected.

 

There are 18.7 retinitis pigmentosa patients per 100,000 people in Japan.

Recent years, artificial retinas have been studied worldwide. 

 

In the United States, Argus II, an electronic retinal implant, has been used since 2013. 

 

Argus II requires an eye surgery for placing an implant on the surface of the retina under general anesthesia.  Argus II uses an external digital camera mounted on eyeglass frames.  Images obtained by the camera are processed by a processor.  The processed signals are sent to a receiver implanted in the patient's face skin.  The signals are sent to electrodes placed near the retina through wires.  The electrodes output currents that stimulate neural cells in the retina to generate stimulation signals.  The generated signals are transmitted to the occipital lobe.  As a result, the patient can have an eyesight to some extent.    

 

However, Argus II has disadvantages of low resolution, narrow view field, complicated eye surgery, and high cost in excess of US$150,000, excluding the cost of the implantation surgery and training.

 

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OURep. Image Source:  Okayama University

 

As a counterpart of Argus II, a research team of Okayama University in Japan has studied an artificial retina named OURep (Okayama University-type retinal prosthesis) since 2002. 

 

OURep is composed of a photoelectric dye-coupled polyethylene film.  The dye molecules on the film generate light-evoked surface potentials and stimulate neural cells that remain on the retina of the patient unlike Argus II where electrodes implanted in the retina output currents.

 

Before the implantation, the film is folded in the shape of a roll so that it is implanted in the retina through a small lesion cut in the eye ball.

 

Since the material of OURep is inexpensive and the film can be implanted by a conventional not-complicated surgery, the cost of OURep is very low (about US$10,000 per eye).   

 

According to the research team, a clinical trial of OURep will start in 2016.